Band pass shock absorber



April 1962 E. SCHNITZER 3,031,181

BAND PASS SHOCK ABSORBER Original Filed Sept. 30, 1957 INVENTOR 2O 26EMANUEL SCHNITZER United States Patent G 3,031,181 BAND PASS SHOCKABSORBER Emanuel Schnitzer, 926 19th St., Newport News, Va. Originalapplication Sept. 30, 1957, Ser. No. 687,310, now

Patent No. 2,923,670, dated Mar. 15, 1960. Divided and this applicationMar. 7, 1960, Ser. No. 13,397

2 Claims. (Cl. 267-64) (Granted under Title 35, US. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This application is a division of my copending application Serial No.687,310, filed September 30, 1957, issued March 15, 1960 as Patent No.2,982,670, which in turn is a continuation-in-part of my copendingapplication Serial No. 528,563, filed August 15, 1955, now Patent No.2,866,633.

This invention relates to shock struts for machine elements and the likewith particular application to shock absorbers including a pistonslidable in a fluid containing cylinder. In conventional shock absorbersof this type, when the piston moves under compression in the cylinder,the fluid is forced through a small orifice in the piston, giving riseto a damping action which is roughly proportional to the square of therelative velocity of piston and cylinder. It is apparent, therefore,that the higher the disturbance frequency, or time rate of change ofloading, the more resistance the absorber exhibits to relative motionuntil at high frequencies it is, in effect, a rigid link.

One of the primary objects of the invention is to filter out, in a shockabsorber, loads from disturbances in certain frequency ranges or havingcertain rates of application while retaining the required load arrestingcharacteristics of conventional shock absorbers in the remainder of thefrequency spectrum.

An object, also, is to provide simplified and improved means for placingthe primary object of the invention into effect.

Another object of the invention is to provide means for utilizing themetering pin of the piston in a conventional piston-cylinder type shockabsorber, both as a control by telescoping displacement and as a loadfiltering device by virtue of its hollow construction permitting fluidflow therethrough.

Still another object is to provide a new and improved shock absorbersensitive not only to displacement of the coacting parts but to thefrequency of the relative movement of the parts.

A further object is to provide an arrangement in shock absorbers inwhich parts may be removed, replaced or adjusted Without the necessityof complete disassembly of the shock absorber strut.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the solitary FIGURE of the accompanying drawing whereinis shown a longitudinal sectional view of the shock absorber, with themetering pin fixed to the base of the absorber cylinder.

Referring now to the drawing, a shock absorber It) is shown adapted forinsertion between machine parts 11 and 12, which may be an airplane bodyand a supporting wheel. This shock absorber is of the plunger typeincluding reciprocatable members 13 and 14 attached respectively toparts 11 and 12, the members 13 and 14, being for example, in the formof hollow cylinders, member 13 telescoping in member 14.

The lower or piston end of piston 13 is provided with an end plate 15,forming a closed surface except for the centrally positioned mainorifice 16. This orifice is one member of a valve mechanism, as will beexplained hereinafter, and to this end the orifice edge is curvedaxially to give a nozzle formation. The base or outer end of theabsorber cylinder 14 is closed by a plate 17, and attached to this plateis a centrally disposed control cylinder 20, a plunger or pin 21extending from the inner top end of the cylinder to and through the mainorifice 16 in piston plate 15, but not contacting the orifice edge, sothat there is a permanent minimum opening about the pin for fluid flow.It is to be understood that the exterior surface of the pin 21 may becontoured so as to vary the effective orifice area as a function of thetelescoping position of the shock strut.

Both control cylinder and pin are hollow, and a function of the controlcylinder is to actuate valve means controlling flow of absorber cylinderfluid through the pin into the absorber piston above plate 15, Toaccomplish this function, a fiat annular disk 22 is provided; the diskhaving a depending edge skirt forming a sliding bearing surface on theinside of cylinder 21). Attached to the central opening edge of thisdisk is a projecting tube 24 terminating in a closed valve element 25adapted to engage the circular inner edge of pin 21. A coil spring 26,mounted inside the control cylinder 20, with ends engaging the outer orlower absorber wall 17 and the valve disk 22, normally hold the valveelement 24 in closed engagement with the pin end, thereby preventingflow therethrough. Connection between the top of control cylinder 20 andthe outer or base end of pin 21 is made by a flared peripheralconnecting section 27 provided With radial slots 28 thereabout for freefluid communication from the shock absorber cylinder 14 to the spaceabout valve element 25. It is apparent that on opening of valve 25,fluid communication is established between the cylinder and pistonthrough pin 21. A bleed orifice is formed in annular valve disc 22 and anon-saturable compressible material such as sponge rubber 30 withnonconnected air holes distributed therein is inserted either in valvetube 24 or somewhere in the control cylinder 20 between plates 22 and17.

In the operation of the described shock absorber, it is assumed that thecylinder 14 is filled with a pressure transmitting fluid 31, such asoil, and the piston 13 is gas-filled, as with air. Preferably the liquidfrom cylinder 14 overflows into piston 13 to cover the main pistonorifice 16, as shown in the drawing. Under the influence of compressionapplied axially to the strut, where there is a slow rate of increase ofthe pressure in the lower cylinder 14, the pressure, building up at aslow rate, forces liquid through the annular space in main orifice 16around the outside tip of pin 21, thus compressing the air in piston 13to absorb shock. The magnitude of the load will be controlled by thetelescoped position or displacement of the strut. Also, fluid will beforced into the control cylinder 20 through the slots 28 at the base ofthe pin and thence through the bleed orifice 29 into the region belowthe valve element 25. Since the pressure increases slowly in cylinder 1the bleed orifice does not present a serious restriction to fluid flowthrough the valve plunger. Consequently, the spring 26 will maintain thevalve in its up or closed position while the volume of compressiblematerial will become smaller as the fluid pressure increases below thevalve element. Thus, this shock strut, for low rates of loading, willbehave in a manner similar to a conventional aircraft shock strut with ametering pin.

For high rates of loading, the bleed orifice 29 will offer seriousresistance to the transfer of fluid into the control cylinder 20 and, inconsequence, the pressure difference above and below the valve disk 22will cause it to move downwardly, opening valve element 25 to flow ofliquid from the absorber cylinder 14, through control cylinder slots 28and pin 21 and into the upper piston 13. Hence, for these higher loadingrates, the load transmission is markedly reduced, the shock absorberbeing efiective for load shock only for the lower predetermined rates ofload application.

It will be apparent to those skilled in the art that damping control inthe described shock absorber is secured through a mechanism sensitivenot only to relative displacement of the absorber elements but also tothe frequency or rate of application of the loads. Since the liquid flowthrough the pin will usually be much greater than that around it, forrapidly applied loads, the rate control will, as a general rule, faroutweigh the displacement control, in alleviating load in this type ofstrut.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A shock absorber adapted for connection between two machine parts fordamping loads of selected rates of application transmitted between saidmachine parts, comprising a hollow cylinder forming a receiver having aclosed base end and adapted to contain a fluid, a hollow cylinderforming a piston having closed ends adapted to contain a gas and havingtelescopic connection with said receiver cylinder to reciprocate in saidreceiver cylinder, the closed piston end within said receiver cylinderhaving a main orifice therein, a control cylinder fixed internally tothe base of said hollow receiver cylinder, a hollow plunger attached tosaid control cylinder for fluid communication with the interior thereof,said plunger having a free end positioned in said closed piston end mainorifice, a valve slidably disposed Within said control cylinderincluding a portion normally positioned to block fluid flow from saidcontrol cylinder into said hollow plunger and an apertured disk portionhaving an annular edge in sliding contact with the interior of the sidewall of said control cylinder, said valve being movable upon thedevelopment of fluid pressure within said receiver at rates above themaximum rate of fluid flow through the apertured disk portion of saidvalve to permit fluid to flow from said control cylinder into saidhollow plunger, a coil spring mounted in said control cylinder betweensaid valve and said base of said hollow receiver cylinder, and aplurality of apertures formed along the wall area of the controlcylinder to permit free flow of fluid therethrough.

2. A shock absorber adapted for connection between two machine parts,comprising a hollow cylinder partially filled with fluid forming apiston connectable to one part, a hollow fluid filled cylinder forming areceiver connectable to the other part, said piston having telescopingconnection with said receiver, a piston head having a main orificetherein at the compression end of said piston, a hollow plunger attachedto said receiver within the interior thereof, said plunger having a freeend positioned In said orifice and a passage way to said receiver spaceat its attached end, and a valve interposed in the flow space betweensaid passage way and plunger interior, said valve including controlmeans comprising an apertured disk movable in a control cylinder uponthe development of fluid pressure in said receiver at a rate above themaximum rate of fluid flow through said apertured disk for actuatingsaid valve to permit fluid flow between said passage way and saidplunger interior.

References Cited in the file of this patent FOREIGN PATENTS 992,347France July 11, 1951

